Screening and comminuting device

ABSTRACT

An improvement in the positioning and cutting of a comminuting and screening device of the type having a rotary screen formed of co-axial rings with outwardly directed cutters which coact with stationary cutters supported on a flow directing enclosure which is positioned in a flow channel by eccentric locks pivoted on the enclosure and frictionally engaging sides of the flow channel, the stationary cutters having a cutting edge coacting with a cutting edge on the end of the screen cutters and a cutting edge extending between the rings, the space between adjacent rings increasing from upstream to downstream sides of the rings.

O United States Patent 11 1 [111 3,893,923 Rudzinski *July 8, 1975 [54] SCREENING AND COMMINUTING DEVICE 2,672,985 3/1954 Nordell 210/ 154 X 374,55 1163 Rd'k'. ..201 [76] Inventor: Stanley P. Rudzinski, 1156 5. 2 2 1 3 1 32 Lombard Oak Park, 60304 3,812,967 5/1974 Rudzinski 210/174 Notice: The portion of the term of this patent subsequent to May 28, 1991, Primary ExaminerThe0d0re A. Granger has been disclaimed.

[22] Filed: May 23, 1974 57 ABSTRACT pp 472,681 An improvement in the positioning and cutting of a Related US Application Data comminuting and screening device of the type having cominuatiomim art of Ser No 329 585 Feb 5 a rotary screen formed of co-axial rings with out- 1973 Pat No 3p812967 wardly directed cutters which coact with stationary cutters supported on a flow directing enclosure which [52] U 5 Cl 210/16l 210 N7 4 is positioned in a flow channel by eccentric locks piv- [51] B61! 33/00 oted on the enclosure and frictionally engaging sides [58] Fie'ld 154 161 of the flow channel, the stationary cutters having a g 6 17 cutting edge coacting with a cutting edge on the end of the screen cutters and a cutting edge extending be- [56] References Cited tween the rings, the space between adjacent rings increasing from upstream to downstream sides of the UNITED STATES PATENTS rings 2,317,416 4/1943 Stanley 210/174 2,336,069 12/1943 Chase 210/174 9 Claims, 7 Drawing Figures SCREENING AND COMMINUTING DEVICE This is a continuation-in-part of application Ser. No. 329,585, filed Feb. 5, 1973, now U.S. Pat. No. 3,812,967.

The present invention relates to improvements in a screening and comminuting device of the type described and claims in my U.S. Pat. No. 3,074,555, issued Jan. 22, 1963 and in my U.S. application for patent Ser. No. 329,585, now U.S. Pat. No. 3,812,967 filed Feb. 5, 1973 of which the present application is a continuation in part.

It is a general object of the present invention to provide a screening and comminuting device for fluid materials which has improved cutting action and more effectively maintains fluid flow for screening action. In carrying out the foregoing, an object of the invention is to provide efficient stationary cutting elements for coaction with movable cutters on a rotary screen such that the elements not only cut material lengthwise of the rotor but also radially thereof. A further object of the invention is to increase the useful screening area of the rotary screen by utilizing the stationary cutting elements to keep the flow openings in the screen free of accumulations of oils, grease and other adherent materials carried by the fluid being treated such that fluid flow and screening action do not decrease when the device is used with fluid contaminated with such materials. It is a related object to maintain the screening and comminuting device in a predetermined, effective position within the fluid flow channel without the necessity of incorporating holding devices on stops in the chan' nel walls.

The foregoing objects and others will become apparent from the specification of which the following is a detailed description of the preferred embodiment of the invention taken in connection with the accompanying drawings in which:

FIG. 1 is a perspective of a screening and comminuting device embodying the present invention and positioned in a portion of an exemplary fluid flow channel; FIG. 2 is a plan of a cover plate for the device of FIG.

FIG. 3 is an exploded partial perspective of a screening element with a cutter and locking device;

FIG. 4 is a partial top view of a screening element with a cutter and locking device assembled;

FIG. 5 is a partial plan view of the cutter arrangement showing screening elements and the relationship of the stationary and movable cutters;

FIG. 6 is a partial plan view of a modified form of stationary cutting element; and

FIG. 7 is a partial perspective of the stationary cutting element of FIG. 6.

Referring to the drawings in more detail, an improved comminuting and screening apparatus 10 embodying the improvement of the present invention is shown adapted for use in a rectangular liquid flow channel 11 which may carry sewage or other fluid having solids which must be comminuted or removed prior to treatment or discharge of the fluid. As shown in FIG. 1, the apparatus comprises a rotor 12, a support structure 13, a drive mechanism 14 and flow directing means. Carried by the rotor 12 and support structure 13 are cooperating movable and stationary cutting elements 17, 18 for cutting and comminuting solids contained in fluid flowing in the channel 11. In the assembly of FIG. 1, the fluid flow is from left to right with the upstream side referred to herein as the front of the device and the downstream side referred to as the rear.

The apparatus of FIG. 1 has a single driven part comprising the rotor 12 carried by a concentric axle or shaft 20 which is supported at its upstream or front end by a bearing or journal 21. The latter in turn is supported at the top of a vertical support column 22. The downstream or rear end of the axle 20 is supported by a like bearing and column, not shown. A detailed description of the rotor, support structure and drive mechanism is set forth in my copending U.S. application Ser. No. 329,585 now U.S. Pat. No. 3,812,967. For present purposes it is sufficient to state that the vertical support columns are rigidly mounted on a fore and aft base plate such that the axis of rotation of the rotor 12 is substantially parallel to the direction of fluid flow in the channel 11. The rotor itself is formed by a series of circular screening bars or rings 24 supported on the axle 20 by ribs 25 which are fixed longitudinally to the axle intermediate the bearings or journals and which are equally spaced around the axle extending radially outwardly therefrom. The screening bars 24 increase in diameter from the upstream to downstream portions of the rotor 12 and are spaced apart axially to form screening apertures or slots therebetween and thus permit fluid flow between them. As best seen in FIG. 5, the screening bars have a cylindrical inner face and a radial rear face which faces are welded or otherwise fixed to stepped portions 26 formed in the ribs 25.

Further in connection with the preferred construction of FIG, 5, the outer faces of the bars 24 are cylindrical with the segments forming the faces lying substantially parallel to the axis of rotation of the rotor 12. In addition, the outer circumference of each bar 24 is larger than the outer circumference of the preceeding upstream bar while its inner circumference is smaller than the outer circumference of the preceding upstream bar. The result is a stepped shape on the outer surface of the rotor so that fluid passing along the outer surface encounters a series of interruptions, that is, the stepped faces of the bars 24, and a turbulent flow results. This construction assists in cleaning the bars of debris screened from the fluid and in redistributing such debris for comminuting by the cutting elements 17, 18. It also causes the fluid flow to bend sharply inwardly in order to pass between the bars further enhancing the screening characteristics of the device.

Surrounding the rotor 12 and supported by the base plate is an arrangement of shields and baffles for directing fluid flow to and through the rotor screen. For this purpose, upright side walls 28, 29 are provided at the side edges of the base plate, and front and rear upright baffles 30, 31 are connected to the base plate as its front and rear eadges. The baffle plates 30, 31 extend crosswise of the width of the channel interconnecting the side walls 28, 29. Both the front and rear baffles have a central opening 33, 34 approximately the size and shape of the largest screening bar of the rotor 12. The rear baffle plate 31 is radially aligned with the rear of rotor 12 and forms therewith a barrier to the passage of fluid such that fluid is forced to pass between the screening bars 24 to reach the downstream end of the device.

For rotating the rotor, suitable drive means such as an electric motor 35 and speed reducing gearing 36 are provided. The motor 35 and gearing 36 are supported on the base plate by a pair of laterally spaced apart upright plates 38 and a motor mounting cross plate 39 secured to the top thereof. Mechanically interconnecting the motor 35 and gearing 36 to the rotor 12 is a belt drive from the motor and gearing to the rear of the rotor. In the illustrative form of the drawings, this includes a drive sprocket 40 connected to the output shaft of the gearing 36 and a roller chain belt 41 interconnecting the drive sprocket 40 and a suitable ring sprocket, not shown, fixed to the rear of the rotor 12. To take up slack in the roller chain belt 41, an idler sprocket 42 journaled on an arm 43 which is pivotally mounted on the rear baffle plate 31 may be incorporated in the drive mechanism.

To provide protection to operators of the device and to protect the device itself from hard objects which might be dropped into it, protective shield means is provided for the rotor 12. In the preferred form of the present invention, the shield means comprises a cover plate 45 extending forwardly above the rotor 12 from the rear baffle plate 31 to above the front end of the rotor 12, and transversely from side to side of the rotor. As illustrated in FIG. 1, the cover plate 45 is supported on the upper edge of the rear baffle plate 31 by a pair of hinges 46. The forward end of the cover plate 45 may be maintained in an elevated position above the rotor 12 by supporting the respective edge portions of the cover on the upper edges or parts thereof of the upright side walls 28, 29, or support may be provided by the upper edge of the front baffle 30 engaging the front edge of the cover. Although a solid cover plate 45 is adequate for normal flow conditions in which the fluid level is well below the top of the baffle structure, a sudden surge of fluid could cause the front end of the cover plate 45 to swing upwardly blocking the upper portion of the channel 11. A preferred form of cover 48 is shown in FIG. 2 in which openings are formed in the cover to permit excess fluid to flow through the cover in unexpected surge conditions without lifting the cover and blocking passage of the excess fluid over the device to the downstream side. The escape openings in the cover plate are so spaced and dimensioned as to intercept solid objects of appreciable size. To accomplish this, a grill type of cover plate 48 is shown in FIG. 2 in which the plate is formed by a peripheral frame of end and side pieces 49, 50 with longitudinal spaced apart ribs or bars 51 extending from end to end to define lengthwise passages therebetween.

A further feature of the improved device of the present invention relates to the provision of means for maintaining the device in a selected position within the flow channel 11. For this purpose, portions of the support structure of the device are provided which project transversely of the channel 11 into close proximity to opposed areas of the respective side walls of the channel. In the embodiment of FIG. 1, such portions of the device are side sections of the front baffle 30 which is formed to extend crosswise of the channel into close relationship to the channel walls. Mounted on the front baffle 30 adjacent its edges are eccentric or cam-like locking members 53. The eccentric members 53 are pivotally mounted on the front baffle plate 30 a fixed distance apart transversely of the channel 1 1 by means of pivot pins 54 projecting forwardly from the front of the baffle at opposite side portions thereof. In the form of FIG. 1, the members 53 comprise portions of an eccentric having a rectangular shape with the pivotal support adjacent one end and a section of the eccentric surface on the edge of the second end. The eccentric end surface may be a sloping end face but preferrably is a curved surface of increasing radii from one side edge to the other. The center of pivoting or swing of the members 53 is positioned such that its distance to the adjacent side wall is greater than the smaller radii of the eccentric end surface but less than that of the larger radii. Thus with both eccentric members 53 extended outwardly the distance between their eccentric end surfaces is greater than the width of the channel 11. By so constructing and pivotally supporting the members 53, the entire device is effectively positioned within the channel by swinging each of the members 53 inwardly and upwardly around the respective pivot pins 54 and then pushing the members downwardly and outwardly until the portions of eccentric ends having the larger radii are pressed against the respective side walls of the channel. The resulting eccentric or cam action due to the increasing radii of the ends of the members and the support given by the front baffle plate 30 against inward movement of the pivots 54 wedges the device in place without the use of bolts, grooves or other fastening means being formed in the channel walls.

To provide the desired comminuting action, the device is provided with a series of movable cutting elements 17 on the outer surface of the rotor 12 and a coacting series of cutting elements 18 supported on the frame of the device. For this purpose, the movable cutting elements or cutters 17 are mounted on the outer surfaces of the screening bars 24 and comprise rectangular bits of cutting material such as hardened steel. The cutting bits 17 have a width to form a cutting edge which is substantially as long as the width'of the screening bar 24. As more fully described in my said application Ser. No. 329,585 now US. Pat. No. 3,812,967, the movable cutting 2its ]re positioned in slots 16 formed in the outer surface of the screening'bars 24, the slots 56 2eing formed crosswise of each bar in a generally fore and ]ft 4irection. The slots 16 Save 4epth less than the height of the cutter bits 17 so that a portion of the bits extends beyond the surface of the screening bar. The leading edge of the extended portion thereby forms a cutting edge. For removably holding the bits 17 in the screening bars 24, the screening bar has an aperture 58 in its outer surface adjacent to each slot 56 as is best seen in FIG. 3. Surrounding the aperture 58 is a counterbore 57 which has a a portion of one side opening into the bit receiving slot 56. Received in the aperture 58 is a locking element or pin 59 which has a cylindrical shank 60 for insertion into the aperture 58 and an enlarged flat head 61 which is positioned in the counterbore 57. The thickness of the head 61 is equal or slightly less than the depth of the counterbore 57 so the the top of the head is generally level with, or slightly below, the outer surface of the screening bar. The periphery of the head 61 is cam shaped, having a portion of reduced radius that extends to the adjacent edge of the bit receiving slot 56, such as the flat portion 62. The remaining portions of the periphery of the head increase in radius to a radius greater than the distance from the shank axis to the ldjacent edge of the slot 56 so that the portions of greater radius overlap the edge. Thus for mounting a cutter bit 17, the locking pint 59 is turned such that the head portion 61 having the smallest radius 62 is toward the slot 56, leaving the slot open for insertion of the bit. The locking pin 59 is then rotated forcing the portions of the head of larger radii against the adjacent side face of the bit 17 and by cam action firmly wedging the bit in place in the slot. Means such as a slot or a polygonal opening 63 in the head of the locking member 59 are provided for turning the locking pin into and out of locking engagement by use of a screwdriver or Allen wrench.

Cooperating with the movable cutters are the stationary cutting elements 18 which are supported on the base support structure 13 in fixed relation to the rotor cutters 17. For this purpose, a horizontal support bar 65 positioned generally at the vertical level of the rotor axis with its inner edge portion extending along the outer face of the rotor 12 in substantially parallel, spaced relation thereto is provided to hold the stationary cutters 18. In the illustrative embodiment of the drawings, the support bar 65 comprises the inner sloping section of a triangular shelf or ledge. The outer side of the shelf is securely supported by the lower portion of one of the upright side panels 28 of the device, while the inwardly projecting enlarged forward portion is supported on the front bearing column 22 by bolts or welding.

To promote efficient comminuting and screening, the stationary cutting elements and screening bars 24 are formed and positioned relative to each other to enhance the trapping and cutting of solids as well as to maintain open areas for the passage of fluid through the rotor screen. To this end, the stationary cutters 18 are positioned along the support bar 65 in fore and aft alignment with respective ones of the screening bars 24. The main portion of each bit 18 is of rectangular shape, one edge of which forms a first cutting edge aligned with, and lying parallel to, the cutting edge of its coacting movable cutting bit 17 on the adjacent screening bar. The stationary bits 18 are mounted on the support bar 65 by means of a bolt 67 which passes through a hole in the center of the bit and is received in a threaded hole in the support bar 65. By rotating the bit 18 about its mounting bolt 67, the first cutting edge may be adjusted to parallel relation with the coacting movable bit 17. By varying the movable bit 17 in or out of the bit receiving slot 56, the spacing between the cutting edges of coacting bits may also be adjusted. The cutting action can be further improved by angling the movable cutting edge of the bits 17 with respect to the direction of movement as shown by the angle A of FIG. 4. The result is a cutting action which progresses along the cutting edge from the leading front corner of the movable bit 17 to its trailing rear corner in a shearing or scissors-like action.

In another aspect of the present invention, the stationary cutters 18 are provided with a radially inwardly extending projection or finger 66 dimensioned to extend radially across one side face of a screening bar and preferably into the space between adjacent screening bars 24. The inward projection 66 presents a second cutting portion along its radially extending edge which faces the corresponding movable cutter 17 such that additional cutting action is provided by appropriately shifting the movable cutter bit axially toward the stationary cutter projection 66. The radial projection or finger 66 also serves to remove solid particles which may become lodged between the screening bars 24 and assists in returning such particles to the upstream side of the rotor where additional cutting or comminuting can take place until the particles are reduced sufficiently in size to pass between the screening bars. Another action of the radial projections 66 is to prevent the build-up of grease, fats and like materials which may be present in the fluid being treated. Such materials have a tendency to adhere to the screening bars and reduce the fluid flow by blocking the screening pas sages. For this purpose, the projections 66 have a length substantially equal to the thickness of the screening rings 24 and preferably extend to within a short distance of the ribs 25.

The stationary cutter bits 18 may if desired by provided with a second projection or finger extending from the diagonally opposite corner of the rectangular body portion of the bit as shown in FIG. 5. The second projection permits reversing the bit to provide a second set of stationary cutting edges after the first set has become worn. The movable cutter bits 17 may also be reversed or rotated in the receiving slots 56 to present a new movable cutting edge after the original edge requires replacement.

In maintaining an open screening area to the passage of fluid, it has been found advantageous to reduce the length of the narrow portion of the passage between adjacent rings by forming a bevel or sloped portion 68 on at least one side of the screening rings 24. In the preferred form shown in FIG. 5, the forward or upstream.

side of the screening rings 24 has a beveled or sloped inner portion 68 of the bar that overlaps or faces the the rear or downstream side of the preceding smaller ring 24. In this manner, the passage between adjacent rings is relatively narrow at the periphery of the preceding smaller ring and increases in width from that periphery or circumference as the passage proceeds radially inwardly. By so shaping the screening bars to provide a passage between the adjacent ones of them which increases in area from the outside to inside of the rotor screen, the radially inward projection on the stationary cutter bits 18 will keep the screening passages open and effective if it extends inwardly at least to the circumference of the next preceding smaller screening bar 24, although preferably the projection 66 extends inwardly to within a short distance of the ribs 25 as previously mentioned.

An alternative form of stationary cutter bit is illustrated in FIGS. 6 and 7. In this form, the inwardly projecting finger 66a is a separate piece of cutting material rather than an integral portion of the cutting bit 18 as shown in FIG. 5. In order to hold the rectangular strip of cutting material which forms the projection or finger 66a in proper relation to the separate cutting bit 18a, a clamping lip 69 formed as a sideward extension of the top portion of the bit 18a overlies the top surface of the finger 66a when the latter is placed along side of the bit. To insure a secure clamping, the finger 66a has a height slightly greater than that of the side of the bit 18a depending from the lip 69 such that the lower edge portion of the finger 66a projects a short distance below the bottom of the bit 18a. On the bottom edge of bit 18a opposite to the side on which the finger 66a is placed, a foot or ridge 70 is provided to maintain the bit level with the support shelf when the finger is inserted. For this purpose the height of the ridge 70 is equal to the amount that the finger 66a projects below the bit 18a. When the finger 66a and bit 18a are correctly assembled and aligned with the coacting movable bit 17, they are secured to the support bar 65 by the bolt 67 or other fastening. The bottom projecting portion of the finger 66a and the foot or ridge 70 on the bit 18a insure that locking force is applied to the finger 66a as well as to the bit 18a to maintain the assembly in proper position for comminuting.

Thus the form of stationary cutter of FIGS. 6 and 7 accomplishes the effective cutting and screening action of the cutters 18 of FIG. and in addition provides flexibility for relative adjustment of the cutting edges of the bit 18a and the finger 66a.

I claim as my invention:

1. In a screening and comminuting device including a rotor having co-axial screening rings spaced apart axially to form fluid passages therebetween, a stationary cutter support bar and support structure for rotatably supporting said rotor in a channel for flow of fluid through said passages and for maintaining said support bar in fixed relation to the upstream surface of said rotor, the combination comprising movable cutter bits mounted on said rings, each bit having a cutting edge portion extending generally axially of the rotor and projecting from the upstream side of said rings, and stationary cutter bits mounted on said support bar, each of said stationary bits having a cutting edge aligned for coaction with said cutting edge of a respective one of said bits on said rings, said stationary bits also having a radially extending portion projecting into a respective one of said passages between adjacent ones of said rings for removing solid material deposited in said passage.

2. The combination of claim 1 in which each of said movable cutter bits has a second cutting edge portion extending generally radially of said rotor toward the passages between said rings, and said radially extending portions on said stationary cutter bits having a second cutting edge extending radially alongside the path of rotary movement of said second cutting edge portion of said movable cutter bits for cutting coaction between said second cutting edges on associated ones of said movable and stationary bits.

3. The combination of claim 1 in which the outer diameter of said screening rings is larger than the outer diameter of the adjacent preceding ring with the inner diameter of said screening rings being smaller than the outer diameter of said adjacent preceding ring, and the outer periphery of each ring is substantially cylindrical such that fluid flowing axially along the outer surface of said rotor flows over a series of steps until it passes through one of said passages.

4. The combination of claim 1 in which said screening rings have radially extending side faces in overlapping relation in a radial direction with said faces on adjacent screening rings for at least part of the width of said faces to define said fluid passages, an overlapping side face of each of said rings sloping away from the overlapping side face on an adjacent ring for at least part of said passage to increase the width of the passage from the upstream to downstream ends thereof.

5. The combination of claim 1 in which the outer diameter of said screening rings is larger than the outer diameter of the adjacent preceding ring with the inner diameter of said screening rings being smaller than the outer diameter of said adjacent preceding ring, said rings having radially extending side faces between said inner and outer diameters in overlapping relation in a radial direction with said side faces on adjacent rings for at least part of the width of said faces to define said fluid passages, an overlapping side face of each of said rings sloping away from the overlapping said face on an adjacent passage to increase the width of the passage from the upstream to downstream ends thereof, and the periphery of said rings in the upstream direction being cylindrical to define a series of steps along the upstream face of said rotor.

6. The combination of claim 1 in which said stationary cutter bit comprises a body portion having a cutting edge aligned for coaction with said cutting edge of a respective one of said bits on said rings, an elongated rectangular finger positioned against a radial side of said body portion for projecting into a respective one of said fluid passages, said body portion having a sideward extension overlying said finger, and means for forcing said sody portion into engagement with said support bar for clamping said finger between said sideward extension and said support bar to hold said body portion and finger in coacting relationship with said respective one of said sits and fluid passages.

7. In a screening and comminuting device including a rotor having co-axial screening rings spaced apart axially to form fluid passages therebetween and carrying movable cutters thereon, a stationary cutter support bar having stationary cutters thereon for coaction with said movable cutters, and support structure for maintaining said support bar in fixed relation to the upstream surface of said rotor and for rotatably supporting said rotor in a channel having opposed upright walls for directing flow of fluid to said device and through said passages, the combination comprising a rigid member fixed to said support structure and extending transversely of said channel with its end portions in close proximity to said channel walls, and means on said transverse member for maintaining said support structure in a predetermined position in said channel including a locking member pivotally supported on said transverse member adjacent an end portion thereof for swing of said locking member toward and away from one of said channel walls, said locking member having an edge portion eccentric with respect to said pivotal support, said eccentric portion increasing from a radius with respect to the pivotal support less than the distance from the ends of the transverse member to the channel walls to a radius greater than said distance so v that swing of the locking member toward said channel wall will wedge the transverse member and the eccentric edge portion securely against the channel walls.

8. The combination of claim 7 in which a pair of said locking members are pivotally supported on said transverse member, one being pivotally supported adjacent each of the ends of said transverse member, said eccentric portion of each member increasing from a radius with respect to the pivotal support less that the distance from the adjacent end of the transverse member to the adjacent channel wall to a radius greater than said distance to provide wedging engagement with each of said side walls of said channel.

9. The combination of claim 8 in which the transverse member is a flow directing baffle plate fixed to said support structure for directing fluid from said channel to said rotor. 

1. IN A CREENING AND COMMINUTING DEVICE INCLUDING A ROTOR HAVING CO-AXIAL CREENING RINGS SPACED APART AXIALLY TO FORM FLUID PASSAGES THEREBETWEEN, A STATIONARY CUTTER SUPPORT BAR AND SUPPORT STRUCTURE FOR ROTATABLY SUPPORTING SAID ROTOR IN A CHANNEL FOR FLOW OF FLUID THROUGH SAID PASSAGES AND FOR MAINTAINING SAID SUPPORT BAR IN FIXED RELATION TO THE UPSTREAM SURFACE OF SAID ROTOR, THE COMBINATION COMPRISING MOVABLE CUTTER BITS MOUNTED ON SAID RINGS, EACH BIT HAVING A CUTTING EDGE PORTION EXTENDING GENERALLY AXIALLY OF THE ROTOR AND PROJECTING FROM THE UPSTREAM SIDE OF SAID RINGS, AND STATIONARY CUTTER BITS MOUNTED ON SAID SUPPORT BAR, EACH OF SAID STATIONARY BITS HAVING A CUTTING EDGE ALIGNED FOR COACTING WITH SAID CUTTING EDGE OF A RESPECTIVE ONE OF SAID BITS ON SAID RINGS, SAID STATIONARY BITS ALSO HAVING A RADIALLY EXTENDING PORTION PROJECTING INTO A RESPECTIVE ONE OF SAID PASSAGES BETWEEN ADJACENT ONES OF SAID RINGS FOR REMOVING SOLID MATERIAL DEPOSITED IN SAID PASSAGE.
 2. The combination of claim 1 in which each of said movable cutter bits has a second cutting edge portion extending generally radially of said rotor toward the passages between said rings, and said radially extending portions on said stationary cutter bits having a second cutting edge extending radially alongside the path of rotary movement of said second cutting edge portion of said movable cutter bits for cutting coaction between said second cutting edges on associated ones of said movable and stationary bits.
 3. The combination of claim 1 in which the outer diameter of said screening rings is larger than the outer diameter of the adjacent preceding ring with the inner diameter of said screening rings being smaller than the outer diameter of said adjacent preceding ring, and the outer periphery of each ring is substantially cylindrical such that fluid flowing axially along the outer surface of said rotor flows over a series of steps until it passes through one of said passages.
 4. The combination of claim 1 in which said screening rings have radially extending side faces in overlapping relation in a radial direction with said faces on adjacent screening rings for at least part of the width of said faces to define said fluid passages, an overlapping side face of each of said rings sloping away from the overlapping side face on an adjacent ring for at least part of said passage to increase the width of the passage from the upstream to downstream ends thereof.
 5. The combination of claim 1 in which the outer diameter of said screening rings is larger than the outer diameter of the adjacent preceding ring with the inner diameter of said screening rings being smaller than the outer diameter of said adjacent preceding ring, said rings having radially extending side faces between said inner and outer diameters in overlapping relation in a radial direction with said side faces on adjacent rings for at least part of the width of said faces to define said fluid passages, an overlapping side face of each of said rings sloping away from the overlapping said face on an adjacent passage to increase the width of the passage from the upstream to downstream ends thereof, and the periphery of said rings in the upstream direction being cylindrical to define a series of steps along the upstream face of said rotor.
 6. The combination of claim 1 in which said stationary cutter bit comprises a body portion having a cutting edge aligned for coaction with said cutting edge of a respective one of said bits on said rings, an elongated rectangular finger positioned against a radial side of said body portion for projecting into a respective one of said fluid passages, said body portion having a sideward extension overlying said finger, and means for forcing said body portion into engagement with said support bar for clamping said finger between said sideward extension and said support bar to hold said body portion and finger in coacting relationship with said respective one of said bits and fluid passages.
 7. In a screening and comminuting device including a rotor having co-axial screening rings spaced apart axially to form fluid passages therebetween and carrying movable cutters thereon, a stationary cutter support bar having stationary cutters thereon for coaction with said movable cutters, and support structure for maintaining said support bar in fixed relation to the upstream surface of said rotor and for rotatably supporting said rotor in a channel having opposed upright walls for directing flow of fluid to said device and through said passages, the combination comprising a rigid member fixed to said support structure and extending transversely of said channel with its end portions in close proximity to said channel walls, and means on said transverse member for maintaining said support structure in a predetermiNed position in said channel including a locking member pivotally supported on said transverse member adjacent an end portion thereof for swing of said locking member toward and away from one of said channel walls, said locking member having an edge portion eccentric with respect to said pivotal support, said eccentric portion increasing from a radius with respect to the pivotal support less than the distance from the ends of the transverse member to the channel walls to a radius greater than said distance so that swing of the locking member toward said channel wall will wedge the transverse member and the eccentric edge portion securely against the channel walls.
 8. The combination of claim 7 in which a pair of said locking members are pivotally supported on said transverse member, one being pivotally supported adjacent each of the ends of said transverse member, said eccentric portion of each member increasing from a radius with respect to the pivotal support less that the distance from the adjacent end of the transverse member to the adjacent channel wall to a radius greater than said distance to provide wedging engagement with each of said side walls of said channel.
 9. The combination of claim 8 in which the transverse member is a flow directing baffle plate fixed to said support structure for directing fluid from said channel to said rotor. 